Will Saletan writes about politics, science, technology, and other stuff for Slate. He’s the author of Bearing Right.

The reason you're reading about Bristol Palin's pregnancy is that she's taking it to term. If she had aborted it, you'd never have known. Which raises the question: How many other daughters of nominees have gotten knocked up without your knowledge?

Let's make a list of unintended-pregnancy candidates going back to, say, 1964. To be conservative, let's draw a ceiling at age 30. That rules out Alexandra Kerry and Rebecca Lieberman, who were 31 when their fathers ran, as well as Dick Cheney's and Lloyd Bentsen's daughters. And let's draw a floor at 17, Bristol Palin's age. That rules out Chelsea Clinton (who was 12 when her dad won), Amy Carter (who was 13 when her dad ran for re-election), and Corinne Quayle (who was 14 when her dad lost). Here's the pared-down list:

Presidents

George W. Bush: Barbara and Jenna were 18 when he was elected.George H. W. Bush: Doro was 21 when he ran for VP with Reagan.Ronald Reagan: Patti was 24 when he ran in 1976 and was 28 when he won in 1980.Gerald Ford: Susan was 17 when he became president and 19 when he ran for re-election.Richard Nixon: Tricia was 22 and Julie was 20 when he won the presidency.Lyndon Johnson: Lynda was 20 and Luci was 17 when he headed the ticket.

Vice Presidents

Al Gore: Karenna was 19 when he ran for VP; Kristin was 19 when he ran for re-election.Walter Mondale: Eleanor was 16 when he ran for VP, 20 when he ran for re-election, and 24 when he ran for president.Bob Dole: Robin was 22 when he ran for VP.Spiro Agnew: Pamela was 25 and Susan was 20 when he ran.Hubert Humphrey: Nancy was 25 when he ran for VP.

Presidential nominees

John Kerry: Vanessa was 27 when he ran. (Alexandra was 31.)Michael Dukakis: Andrea was 22, and Kara was 20.George McGovern: Ann was 27, Susan was 26, Terry was 23, and Mary was 17.Barry Goldwater: Joanne was 28, and Peggy was 20.

Vice-presidential nominees

John Edwards: Cate was 22 when he ran with Kerry.Jack Kemp: Jennifer was 25 and Judith was 23 when he ran for president.Geraldine Ferraro: Donna was 22 and Laura was 18 when their mom ran with Mondale.Sargent Shriver: Maria was 17 when he ran with McGovern.Ed Muskie: Ellen was 18 when he ran with Humphrey.Bill Miller: His eldest daughters were 20 and 17 when he ran with Goldwater.

I count 34 eligible females on that list. If you throw in Joe Biden's 27-year-old daughter and John McCain's 24- and 17-year-old daughters, the total is 37.

Next question: What are the U.S. pregnancy rates in these age brackets?

Pregnancy rates vary by year but not stupendously. According to government data released in April, the most recently calculated pregnancy rate among women aged 25 to 29 was 17 percent. Among women 20 to 24, it was 16 percent. Among teens 18 to 19, it was 12 percent.

Of course, presidential and vice-presidential families aren't normal. They're wealthier and better-educated than most of us. So let's factor that in. According to a 2006 analysis by the Alan Guttmacher Institute, overall U.S. pregnancy rates in 1994 and 2001 were 10 percent to 11 percent, but the rates in families with incomes at least twice the poverty level were 8 percent to 9 percent, and the rates among college graduates were 10 percent to 11 percent.

If we limit our focus to unintended pregnancies, the numbers come down significantly. Only 3 percent to 4 percent of women in the higher income bracket had unintended pregnancies in the two sampled years. On the other hand, the unintended pregnancy rate in the 18-29 age bracket is nearly double the overall unintended pregnancy rate. So if you factor age into the equation, the rate of unintended pregnancy among 18- to 29-year-olds in the higher income bracket is probably around 6 percent to 7 percent.

An unintended pregnancy rate of 6 to 7 percent, in a population of 37 women, means two to three pregnancies per year. Even if you discount the rate further, on the grounds that these are the wealthiest and best-educated families, the notion that none of these young women got knocked up before their parents' nominations or elections is—pardon the term—almost inconceivable. If you're a politician, and your daughter gets pregnant out of wedlock, you can be systematically excluded from the sample of nominees by self-selection, voters, or running-mate vetters. But not if the pregnancy never becomes known.

If any of these daughters conceived, but no pregnancy or birth was reported, what happened? One possibility is miscarriage. But the Guttmacher analysis suggests a different answer: Most unintended pregnancies in the higher income and education brackets end in abortion.

Remember that before you judge or poke fun at Sarah Palin. She's not the candidate whose daughter messed up. She's the candidate who didn't get rid of the mess.